*** a/doc/src/sgml/func.sgml
--- b/doc/src/sgml/func.sgml
***************
*** 12793,12798 **** postgres=# SELECT * FROM unnest2(ARRAY[[1,2],[3,4]]);
--- 12793,12805 ----
        </row>
  
        <row>
+        <entry><literal><function>pg_trigger_depth()</function></literal></entry>
+        <entry><type>int</type></entry>
+        <entry>current nesting level of <productname>PostgreSQL</> triggers
+        (0 if not called, directly or indirectly, from inside a trigger)</entry>
+       </row>
+ 
+       <row>
         <entry><literal><function>session_user</function></literal></entry>
         <entry><type>name</type></entry>
         <entry>session user name</entry>
*** a/src/backend/commands/trigger.c
--- b/src/backend/commands/trigger.c
***************
*** 60,65 ****
--- 60,68 ----
  int			SessionReplicationRole = SESSION_REPLICATION_ROLE_ORIGIN;
  
  
+ /* How many levels deep into trigger execution are we? */
+ static int	MyTriggerDepth = 0;
+ 
  #define GetModifiedColumns(relinfo, estate) \
  	(rt_fetch((relinfo)->ri_RangeTableIndex, (estate)->es_range_table)->modifiedCols)
  
***************
*** 1838,1844 **** ExecCallTriggerFunc(TriggerData *trigdata,
  
  	pgstat_init_function_usage(&fcinfo, &fcusage);
  
! 	result = FunctionCallInvoke(&fcinfo);
  
  	pgstat_end_function_usage(&fcusage, true);
  
--- 1841,1858 ----
  
  	pgstat_init_function_usage(&fcinfo, &fcusage);
  
! 	MyTriggerDepth++;
! 	PG_TRY();
! 	{
! 		result = FunctionCallInvoke(&fcinfo);
! 	}
! 	PG_CATCH();
! 	{
! 		MyTriggerDepth--;
! 		PG_RE_THROW();
! 	}
! 	PG_END_TRY();
! 	MyTriggerDepth--;
  
  	pgstat_end_function_usage(&fcusage, true);
  
***************
*** 4632,4634 **** AfterTriggerSaveEvent(EState *estate, ResultRelInfo *relinfo,
--- 4646,4655 ----
  							 &new_event, &new_shared);
  	}
  }
+ 
+ 
+ Datum
+ pg_trigger_depth(PG_FUNCTION_ARGS)
+ {
+ 	PG_RETURN_INT32(MyTriggerDepth);
+ }
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
***************
*** 2695,2700 **** DESCR("statistics: reset collected statistics for a single table or index in the
--- 2695,2703 ----
  DATA(insert OID = 3777 (  pg_stat_reset_single_function_counters	PGNSP PGUID 12 1 0 0 0 f f f f f v 1 0 2278 "26" _null_ _null_ _null_ _null_	pg_stat_reset_single_function_counters _null_ _null_ _null_ ));
  DESCR("statistics: reset collected statistics for a single function in the current database");
  
+ DATA(insert OID = 2040 (  pg_trigger_depth				PGNSP PGUID 12 1 0 0 0 f f f t f s 0 0 23 "" _null_ _null_ _null_ _null_ pg_trigger_depth _null_ _null_ _null_ ));
+ DESCR("statistics: current trigger depth");
+ 
  DATA(insert OID = 3778 ( pg_tablespace_location PGNSP PGUID 12 1 0 0 0 f f f t f s 1 0 25 "26" _null_ _null_ _null_ _null_ pg_tablespace_location _null_ _null_ _null_ ));
  DESCR("tablespace location");
  
*** a/src/include/commands/trigger.h
--- b/src/include/commands/trigger.h
***************
*** 205,208 **** extern bool RI_Initial_Check(Trigger *trigger,
--- 205,210 ----
  
  extern int	RI_FKey_trigger_type(Oid tgfoid);
  
+ extern Datum pg_trigger_depth(PG_FUNCTION_ARGS);
+ 
  #endif   /* TRIGGER_H */
*** a/src/test/regress/expected/triggers.out
--- b/src/test/regress/expected/triggers.out
***************
*** 1443,1445 **** NOTICE:  drop cascades to 2 other objects
--- 1443,1562 ----
  DETAIL:  drop cascades to view city_view
  drop cascades to view european_city_view
  DROP TABLE country_table;
+ -- Test pg_trigger_depth()
+ create table depth_a (id int not null primary key);
+ NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "depth_a_pkey" for table "depth_a"
+ create table depth_b (id int not null primary key);
+ NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "depth_b_pkey" for table "depth_b"
+ create table depth_c (id int not null primary key);
+ NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "depth_c_pkey" for table "depth_c"
+ create function depth_a_tf() returns trigger
+   language plpgsql as $$
+ begin
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   insert into depth_b values (new.id);
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   return new;
+ end;
+ $$;
+ create trigger depth_a_tr before insert on depth_a
+   for each row execute procedure depth_a_tf();
+ create function depth_b_tf() returns trigger
+   language plpgsql as $$
+ begin
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   begin
+     execute 'insert into depth_c values (' || new.id::text || ')';
+   exception
+     when sqlstate 'U9999' then
+       raise notice 'SQLSTATE = U9999: depth = %', pg_trigger_depth();
+   end;
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   if new.id = 1 then
+     execute 'insert into depth_c values (' || new.id::text || ')';
+   end if;
+   return new;
+ end;
+ $$;
+ create trigger depth_b_tr before insert on depth_b
+   for each row execute procedure depth_b_tf();
+ create function depth_c_tf() returns trigger
+   language plpgsql as $$
+ begin
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   if new.id = 1 then
+     raise exception sqlstate 'U9999';
+   end if;
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   return new;
+ end;
+ $$;
+ create trigger depth_c_tr before insert on depth_c
+   for each row execute procedure depth_c_tf();
+ select pg_trigger_depth();
+  pg_trigger_depth 
+ ------------------
+                 0
+ (1 row)
+ 
+ insert into depth_a values (1);
+ NOTICE:  depth_a_tr: depth = 1
+ NOTICE:  depth_b_tr: depth = 2
+ CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_c_tr: depth = 3
+ CONTEXT:  SQL statement "insert into depth_c values (1)"
+ PL/pgSQL function "depth_b_tf" line 5 at EXECUTE statement
+ SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  SQLSTATE = U9999: depth = 2
+ CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_b_tr: depth = 2
+ CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_c_tr: depth = 3
+ CONTEXT:  SQL statement "insert into depth_c values (1)"
+ PL/pgSQL function "depth_b_tf" line 12 at EXECUTE statement
+ SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ ERROR:  U9999
+ CONTEXT:  SQL statement "insert into depth_c values (1)"
+ PL/pgSQL function "depth_b_tf" line 12 at EXECUTE statement
+ SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ select pg_trigger_depth();
+  pg_trigger_depth 
+ ------------------
+                 0
+ (1 row)
+ 
+ insert into depth_a values (2);
+ NOTICE:  depth_a_tr: depth = 1
+ NOTICE:  depth_b_tr: depth = 2
+ CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_c_tr: depth = 3
+ CONTEXT:  SQL statement "insert into depth_c values (2)"
+ PL/pgSQL function "depth_b_tf" line 5 at EXECUTE statement
+ SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_c_tr: depth = 3
+ CONTEXT:  SQL statement "insert into depth_c values (2)"
+ PL/pgSQL function "depth_b_tf" line 5 at EXECUTE statement
+ SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_b_tr: depth = 2
+ CONTEXT:  SQL statement "insert into depth_b values (new.id)"
+ PL/pgSQL function "depth_a_tf" line 4 at SQL statement
+ NOTICE:  depth_a_tr: depth = 1
+ select pg_trigger_depth();
+  pg_trigger_depth 
+ ------------------
+                 0
+ (1 row)
+ 
+ drop table depth_a, depth_b, depth_c;
+ drop function depth_a_tf();
+ drop function depth_b_tf();
+ drop function depth_c_tf();
*** a/src/test/regress/sql/triggers.sql
--- b/src/test/regress/sql/triggers.sql
***************
*** 961,963 **** SELECT * FROM city_view;
--- 961,1027 ----
  
  DROP TABLE city_table CASCADE;
  DROP TABLE country_table;
+ 
+ 
+ -- Test pg_trigger_depth()
+ 
+ create table depth_a (id int not null primary key);
+ create table depth_b (id int not null primary key);
+ create table depth_c (id int not null primary key);
+ 
+ create function depth_a_tf() returns trigger
+   language plpgsql as $$
+ begin
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   insert into depth_b values (new.id);
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   return new;
+ end;
+ $$;
+ create trigger depth_a_tr before insert on depth_a
+   for each row execute procedure depth_a_tf();
+ 
+ create function depth_b_tf() returns trigger
+   language plpgsql as $$
+ begin
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   begin
+     execute 'insert into depth_c values (' || new.id::text || ')';
+   exception
+     when sqlstate 'U9999' then
+       raise notice 'SQLSTATE = U9999: depth = %', pg_trigger_depth();
+   end;
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   if new.id = 1 then
+     execute 'insert into depth_c values (' || new.id::text || ')';
+   end if;
+   return new;
+ end;
+ $$;
+ create trigger depth_b_tr before insert on depth_b
+   for each row execute procedure depth_b_tf();
+ 
+ create function depth_c_tf() returns trigger
+   language plpgsql as $$
+ begin
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   if new.id = 1 then
+     raise exception sqlstate 'U9999';
+   end if;
+   raise notice '%: depth = %', tg_name, pg_trigger_depth();
+   return new;
+ end;
+ $$;
+ create trigger depth_c_tr before insert on depth_c
+   for each row execute procedure depth_c_tf();
+ 
+ select pg_trigger_depth();
+ insert into depth_a values (1);
+ select pg_trigger_depth();
+ insert into depth_a values (2);
+ select pg_trigger_depth();
+ 
+ drop table depth_a, depth_b, depth_c;
+ drop function depth_a_tf();
+ drop function depth_b_tf();
+ drop function depth_c_tf();